keep the tray, much stronger and more usefull.!!!!!! if you put a tub on it, you will be limited to what you carry to the width of the tub, but with a tray you cn take the sides off and carry something wider,
and if you do any amount of offroading you wil bend a tub very very easily, but a tray now there is a usefull pice of steel,
i have run my 73s tray into a tree backwards, accidentaly cause i didnt use the stall stop technique, and rolled backwayrds(very very dangerous) hit a tree with my tray, and i got not one iota of damage apart from the pins that keep the side un, bengine ever so slightly
http://www.outerlimits4x4.com/ftopic176184-0-asc-60.php
take a look at my tread, it will give you an idea of a strong working tray, i plan to replace it with a more off road functional tray soon enough.....